In the known state of the art, seismic data are collected by networks of electronic sensor units, which are connected to a central processing server.
Each sensor unit comprises at least one sensor located within a housing, which features a bottom surface intended to be mechanically coupled with the ground. To this end, a sensor unit is usually equipped with a coupling device having the shape of a spike, which is to be buried into the ground. Such a spike is described in a French patent application FR 2918462.
Such a solution is not entirely satisfactory. It has proven impractical in applications where the ground is too hard for a spike to be buried into it, as is the case on urban premises. In such a situation, the sensor unit will have to be simply laid down on the ground and will thus be very unstable, the end result being that the measurements it will take will probably be inaccurate.
For similar reasons, the known solution is impractical when used in arctic conditions. Specially adapted spikes have been designed for such conditions, but these special spikes are very heavy and therefore are detrimental to operational efficiency.
Furthermore, a spike-shaped coupling device may be insufficiently effective to ensure sensor stability in loose soil, e.g. when the ground is made of sand or mud, in which case the spike won't be maintained in position as well as it would be in a more dense, and thus less shifting, environment.
In order to solve this stability problem, additional pedestals in the form of tripods or quadripods are sometimes used, but such pedestals have a tendency to resonate on their own modes and produce non-desired resonant frequencies, which is detrimental to the operational efficiency of the sensor. These non-desired resonant frequencies (noise) would pollute the measured data consequently especially if said sensor is a digital seismic sensor because of their high sensitivity to noise.
Some known sensor units are equipped with a housing featuring a cylindrical pod protruding from the housing's bottom, the spike then being fastened to the end of said pod. In such sensor units, the actual sensor is located in the pod, and thus will be located underground after the spike is properly buried into the ground. In such a configuration, the sensor will be less sensitive to surface noise. However, this design presents a drawback due to the elongated shape of the pod protruding from the housing's bottom, which will tend to resonate at a frequency comprised within the bandwidth under study and may thus significantly alter the operational performance of the sensor unit.